The invention relates to a process for reactivating deactivated catalysts, the reactivated catalysts produced by the process, and the use of the reactivated catalysts in acid catalyzed chemical conversion processes, such as hydrocarbon conversion processes. The invention is particularly concerned with reactivating deactivated hydrocracking catalysts which comprise a crystalline molecular sieve, a Group VIII noble metal hydrogenation component and carbonaceous deposits, and the use of the reactivated catalysts in hydrocracking processes, particularly hydrocracking in the substantial absence of ammonia.
Petroleum refiners often produce desirable products, such as gasoline and turbine fuel, by catalytically hydrocracking high boiling hydrocarbons into product hydrocarbons of lower average molecular weight and boiling point. Hydrocracking is generally accomplished by contacting, in an appropriate reactor vessel, a gas oil or other hydrocarbon feedstock with a suitable hydrocracking catalyst under appropriate conditions, including an elevated temperature and an elevated pressure and the presence of hydrogen, such that a hydrocarbon product is obtained containing a substantial portion of a desired product boiling in a specified range, as for example, a heavy gasoline boiling in the range of 185.degree. to 420.degree. F.
Oftentimes, hydrocracking is performed in conjunction with hydrotreating, usually by a method referred to as "integral operation." In this process, the hydrocarbon feedstock, usually a gas oil containing a substantial proportion of components boiling above a desired end point, as for example, 420.degree. F. in the case of certain gasolines, is introduced into a catalytic hydrotreating zone wherein, in the presence of a suitable catalyst, such as a zeolite- or sieve-free, particulate catalyst comprising a Group VIII metal component and a Group VIB metal component on a porous, inorganic, refractory oxide support most often composed of alumina, and under suitable conditions, including an elevated temperature (e.g., 400.degree. to 1000.degree. F.) and an elevated pressure (e.g., 100 to 5000 p.s.i.g.) and with hydrogen as a reactant, the organonitrogen components and the organosulfur components contained in the feedstock are converted to ammonia and hydrogen sulfide, respectively. Subsequently, the entire effluent removed from the hydrotreating zone is treated in a hydrocracking zone maintained under suitable conditions of elevated temperature, pressure, and hydrogen partial pressure, and containing a suitable hydrocracking catalyst, such that a substantial conversion of high boiling feed components to product components boiling below the desired end point is obtained. Usually, the hydrotreating and hydrocracking zones in integral operation are maintained in separate reactor vessels, but, on occasion, it may be advantageous to employ a single, downflow reactor vessel containing an upper bed of hydrotreating catalyst particles and a lower bed of hydrocracking particles. Examples of integral operation may be found in U.S. Pat. Nos. 3,132,087, 3,159,564, 3,655,551, and 4,040,944, all of which are herein incorporated by reference in their entireties.
In some integral operation refining processes, and especially those designed to produce gasoline from the heavier gas oils, a relatively high proportion of the product hydrocarbons obtained from integral operation will have a boiling point above the desired end point. For example, in the production of a gasoline product boiling in the C.sub.4 to 420.degree. F. range from a gas oil boiling entirely above 570.degree. F., it may often be the case that as much as 30 to 60 percent by volume of the products obtained from integral operation boil above 420.degree. F. To convert these high boiling components to hydrocarbon components boiling below 420.degree. F., the petroleum refiner separates the 420.degree. F.+ high boiling components from the other products obtained in integral operation, usually after first removing ammonia by a water washing operation, a hydrogen-containing recycle gas by high pressure separation, and an H.sub.2 S-containing, C.sub.1 to C.sub.3 low BTU gas by low pressure separation. This 420.degree. F+ boiling bottom fraction is then subjected to further hydrocracking, either by recycle to the hydrocracking reactor in single stage operation or by introduction into a second hydrocracking zone wherein yet more conversion to the desired C.sub.4 to 420.degree. F. product takes place.
In the foregoing two-stage process, the two hydrocracking reaction zones can contain hydrocracking catalysts of the same or different composition. One catalyst suitable for use in both reaction zones is disclosed as Catalyst A in Example 16 of U.S. Pat. Nos. 3,897,327 and 3,929,672, both of which are herein incorporated by reference in their entireties, which catalyst is comprised of a palladium-exchanged, steam-stabilized Y zeolite hydrocracking component. But although the catalysts used in the two hydrocracking reaction zones may have the same composition and the same catalytic properties, the hydrocracking conditions required in the second hydrocracking reaction zone are less severe than those required in the first. The reason for this is that ammonia is not present in the second hydrocracking reaction zone (due to water washing) whereas a significant amount of ammonia is present in the first hydrocracking zone. To account for the difference in operating conditions, it is believed that ammonia neutralizes or otherwise interferes with the acidity of the zeolite in the catalyst of the first reaction zone, thereby forcing the refiner to employ relatively severe conditions for operation, as for example, increased temperature. On the other hand, in the ammonia-deficient atmosphere of the second hydrocracking reaction zone, high conversions to the desired product are obtainable under relatively moderate conditions, often with an operating temperature about 100.degree. to 210.degree. F. lower than that required in the first hydrocracking reaction zone.
Further description of two-stage hydrocracking operations may be found in U.S. Pat. Nos. 4,429,053 and 4,857,169 herein incorporated by reference in their entireties, which patents provide process flow sheets for typical two-stage hydrocracking processes.
Although hydrocracking catalysts containing noble metal-exchanged zeolites are effective for use in single stage hydrocracking as discussed above or in either the first or second stage of the two-stage process discussed above, the activity of such catalysts is diminished during the course of hydrocracking as coke materials deposit on the catalyst particles and interfere with the activity of the catalyst. It is thus necessary to periodically regenerate the catalyst by combusting these carbonaceous deposits, usually at temperatures between 700.degree. and 925.degree. F. It has been found, however, that, after regeneration at temperatures in this range, the catalyst used in the second hydrocracking reaction zone loses substantial activity for hydrocracking under the relatively moderate conditions employed therein.
Many attempts have been made to overcome the detrimental effects associated with regenerating hydrocracking catalysts for use in the ammonia-deficient environments of the second hydrocracking zone, in particularly with respect to catalysts containing noble metal-exchanged zeolites. These attempts have largely focused on methods for restoring some or all of the catalytic activity lost through regeneration by treating the regenerated catalyst with an ammonium salt, ammonium hydroxide, gaseous ammonia, or mixtures thereof, thereby rejuvenating the catalyst. The general theory behind these methods is that the activity losses of catalysts used in hydrocracking environments are caused by the agglomeration of the otherwise dispersed noble metal hydrogenation component, and the ammonia ion treatments redisperse the noble metal component.
Although the above-discussed methods of regeneration and rejuvenation of catalysts containing noble metal-exchanged zeolites have met with some success, the results have not been consistent. For example, in various instances regeneration has resulted in "reactivated" catalysts that range from about 60.degree. to 110.degree. F. less active than the fresh catalyst for hydrocracking under second stage conditions, i.e., hydrocracking in an ammonia-deficient atmosphere. Furthermore, for catalysts which can withstand rejuvenation utilizing ammonia or ammonium ion treatments without collapse of the zeolitic crystal structure, regeneration followed by rejuvenation has resulted in reactivated catalysts that are between 10.degree. F. and 35.degree. F. less active than the fresh catalyst for hydrocracking under second stage conditions.
Accordingly, it should be clear that new methods for reactivating deactivated noble metal-exchanged zeolitic catalysts, particularly hydrocracking catalysts, are needed so that their catalytic activity is substantially restored to the activity of the fresh catalyst prior to deactivation.